[aat] Fix more builds

Maybe I should disable C++11 detection such that my compiler also catches
these.  Doesn't look like we can switch to it for a while anyway...

src/hb-aat-layout-common-private.hh

@@ -637,7 +637,7 @@ struct StateTableDriver
 
       c->transition (this, entry);
 
-      if (entry->flags & context_t::Flags::DontAdvance)
+      if (entry->flags & context_t::DontAdvance)
 	buffer->idx--; /* TODO Detect infinite loop. */
 
       state = entry->newState;